In one known process, polyurethanes containing inter alia terminal hydroxyl and/or amino groups are reacted with cyclic carboxylic acid anhydrides such as benzene tetracarboxylic acid anhydride, in order to introduce into the polyurethane carboxylic acid groups capable of salt formation (see e.g., German Pat. No. 1,237,306).
It is also known that polyurethane ionomers can be produced from prepolymers. Anionic segmented polyurethane ionomers can thus be produced by reacting NCO-terminated prepolymers with bifunctional anionic chain extenders such as diamino or dihydroxy carboxylic acids in accordance with the following equation (see, e.g. German Offenlegungsschrift 1,544,892): ##STR1## Unfortunately, this reaction is difficult to control because the free carboxyl groups are able to react with the isocyanate groups. In some cases, insoluble internal salts are even formed. Accordingly, the anionic component is preferably used in the form of the sodium or potassium salt. The chain extension of NCO-prepolymers with salts of aliphatic diamino carboxylic acids has proved to be the most favorable in this case, polyaddition to form the macromolecule taking place over a short period.
Accordingly, the object of the instant invention is to provide a simplified process for the production of polyureas which results in polyadducts which contain free carboxyl groups and which may be converted into polyureas dispersible in water by simply forming salts from these free carboxyl groups by treatment with suitable bases.